The invention relates to a sensor arrangement for a wheelchair wheel, which has a running wheel that includes a hub and a hand rim. The sensor arrangement includes a running wheel fastening arrangement that can be fastened to the running wheel, a hand rim fastening arrangement that can be fastened to the hand rim and at least one sensor that detects a movement of the hand rim fastening arrangement relative to the running wheel fastening arrangement.
It is known to provide a sensor arrangement between a hand rim and a running wheel of a wheelchair wheel. The sensor arrangement makes it possible to detect when a user of the wheelchair moves the hand rim fastening arrangement, which is fastened to the hand rim relative to the running wheel fastening arrangement. If the user actuates the hand rim of the wheelchair wheel by exerting a tangential force on it in order to move forward or backward, this is registered by the sensor arrangement. The sensor arrangement sends a signal commensurate with the actuation to a drive unit of the wheelchair. The drive unit then assists the movement of the wheelchair wheel.
A sensor arrangement of this type is disclosed, for example, by DE 20 2009 009 929 U1. Upon actuation of the hand rim that is connected to the known sensor arrangement, a hand rim fastening arrangement is moved relative to a running wheel fastening arrangement. The hand rim fastening arrangement is connected to the running wheel fastening arrangement by means of at least two parallel bending plates. After the hand rim is released, the two bending plates return the hand rim fastening arrangement to a zero position relative to the running wheel fastening arrangement. Depending on how far the hand rim is moved from its zero position, an overshooting can occur during the restoring of the hand rim fastening arrangement. It is therefore difficult to reach an exact zero position of the hand rim fastening arrangement relative to the running wheel fastening arrangement.
For that matter, in very old, known sensor arrangement, i.e., with heavily fatigued bending plates, reaching a zero position after the release of the hand rim may not even be possible.
Finally, the known sensor arrangement is situated between the rim of the running wheel and the hand rim. Both the running wheel rim and the hand rim generally have irregularities and tolerances that significantly complicate the task of fastening the known sensor arrangement in position. The fastening options of the known sensor arrangement also are limited by the arrangement of the spokes of the running wheel.
DE 198 48 530 C1 discloses a control device configured for auxiliary drive units of self-propelled wheelchairs and is likewise equipped with a sensor arrangement. The sensor arrangement includes an armature that is supported so that it is able to pivot in a limited fashion, which is used to detect a movement of the hand rim relative to the running wheel. Two lateral arms of the armature are each acted on by a respective spring element that returns the armature to a zero position after the end of an exertion of a force on the hand rim. In this sensor arrangement, it is difficult to define and reliably reach the zero position of the sensor arrangement, depending on the design and fatigue of the spring elements. Finally, this known sensor arrangement is also situated between the rim of the running wheel and the hand rim. As such, irregularities and tolerances of the hand rim and the running wheel rim complicate the task of fastening the known sensor arrangement in position.
DE 20 2008 017 258 U1 also discloses a sensor arrangement in which an actuation of a hand rim moves a magnet in the vicinity of a Hall sensor. Two spring elements are arranged between the hand rim and the Hall sensor and move the hand rim back into a zero position after an actuation. Here, too, the problem arises that if the spring elements are fatigued, the zero position cannot be defined and reproducibly reached, after actuation of the hand rim.
Another example of a sensor arrangement between a hand rim and a running wheel is disclosed in EP 0 832 632 B1. The known sensor arrangement is integrated into the hub of the running wheel. An actuation of the hand rim, which has a significantly larger diameter than the hub, therefore results in only a small movement of the sensor arrangement integrated into the hub. The signal detected by the sensor arrangement is consequently relatively weak in relation to the movement of the hand rim. Two helical springs situated one inside the other restore the sensor arrangement after an actuation of the hand rim. A zero position of the sensor arrangement is reached in that the two end surfaces of a split inner sleeve in which the helical springs are situated rest against two stops of an outer sleeve in which the inner sleeve is in turn situated. The design of the known sensor arrangement with the outer sleeve, the split inner sleeve situated therein and the helical springs contained inside, however, can only be produced and assembled with difficulty.